Solid-state alternating copolymerization took place by molecular oxygen insertion in the crystals of 7,7,8,8-tetrakis(ethoxycarbonyl)quinodimethane (1a) and 7,7-bis(ethoxycarbonyl)-8,8-bis-(methoxycarbonyl)quinodimethane (1b) to form highly crystalline needlelike white solids for 1a and amorphous ones for 1b. The polymer structures were confirmed by 1 H NMR, 13 C NMR, IR, elemental analysis, powder XRD, and TGA measurements. However, in vacuo polymerizations of 1a and 1b in the solid state with heating and photoirradiation did not take place. 7,7,8,8-Tetrakis(methoxycarbonyl)-quinodimethane (1c) did not undergo solid-state alternating copolymerization with oxygen even in the presence of oxygen, but instead it homopolymerized to form highly crystalline homopolymer. The difference in the solid-state polymerization reactivity was discussed on the basis of molecular packing in the crystals obtained by X-ray crystallography. In addition, it was found by ESR measurement that the solid-state alternating copolymerizations with molecular oxygen proceed by means of a radical mechanism.
IntroductionSolid-state polymerization implies that polymerization proceeds starting from bulk monomer crystals, and it has been divided into two classes: topotactic and topochemical polymerizations. 1 The former is the polymerization that provides a polymer with a specific crystal structure formed under control of the crystal lattice of the monomer, and the latter is the polymerization that proceeds with no movement of the center of gravity of the monomer molecule and only slight rotation of the monomer molecule around the gravity; that is, the crystallographic position and symmetry of the monomer crystals are retained in the resulting polymer crystals. Therefore, topochemical polymerization is a promising method to obtain polymers with highly controlled structures. A limited number of monomers such as derivatives of diacetylene, 1 2,5-distyrylpyrazine, 2 triene and triacetylene, 3 muconic acid and sorbic acid, 4 and 7,7,8,8-tetrakis(alkoxycarbonyl)quinodiemthane 5 have been reported to undergo topochemical polymerizations, and they are known to have strict requirements of the monomer arrangements in the crystals. However, it is still difficult to predict and control the polymerization properties of compounds in the crystals because arrangements of monomers play a significant role. Further investigation of the crystal structures of monomers related with solid-state polymerizations should enable us to control the reactivities of the monomers and provide us models for the reaction pathway of the polymerization reactions.
